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Generating Electricity – Revision Pack (P2)
Bigger Currents and Voltages:
A dynamo is a small generator sometimes
fitted to bicycles for light during the night.
Inside the dynamo, there is a permanent
magnet that is rotated in the middle of some
coils of wire.
The rotation of the magnet causes a change
in the magnetic field which generates
electricity in the coils of wire.
You can increase the current of a dynamo
by:
- Using a stronger magnet
- Increasing the number of turns on the
coil
- Rotating the magnet faster
The output from a dynamo can be displayed on an oscilloscope which shows
how the current produced by the dynamo varies with time. The time for one
complete cycle is called the period of alternating current – this is represented
by the length of one wave. The height of the wave is the maximum voltage.
Practical Generators:
A simple generator consists of a coil of wire
rotating between the poles of a magnet:
- The coil cuts through the magnetic
field as it spins
- A current is subsequently produced
in the coil
A current can also be generated if the coil
is stationary and the magnets move.
Power Stations:
Generators in power stations work in the
same principle.
In a conventional power station, electricity is generated in a few simple steps:
STEP 1 – Water boils to produce steam
STEP 2 – Steam at high pressure turns a turbine
STEP 3 – The turbine drives a generator
Generating Electricity – Revision Pack (P2)
Energy efficiency:
Efficiency is a measure of how well a device transfers energy.
In a power station, energy is lost at each stage (in the boiler, generator, and
the cooling towers).
Efficiency can be calculated using the following equation:
Efficiency = useful energy output
Total energy input
Generating Electricity – Revision Pack (P2)
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